A £20,000 reward for information has been announced in the murder investigation of a primary school teacher 20 years ago in her own home.

The reward is for help leading to the arrest and successful prosecution of the person or people responsible for stabbing and sexually assaulting Joy Hewer in her flat in Wood Street, Walthamstow, in October 17, 1995.

Joy, a devout Christian, was 52 at the time of her death.

She had worked locally as a much-loved primary school teacher, most notably at nearby Woodhouse Primary School.

After retirement in 1990 she worked relentlessly to raise money for local charities and church organisations.

Detective Inspector Susan Stansfield, of the Met's Special Casework Investigation Team, who is leading the investigation, said: "Joy was a much-loved daughter and sister and lived a quiet peaceful life.

"She must have suffered greatly at the hands of her attacker and we hope that this latest appeal, coupled with the significant police reward of £20,000, will urge anyone who can help to contact us."

Joy's sister, Penny Barnes, said: "We've waited so long for answers but we'll never give up hope.

"Someone has evaded us for two decades but this latest appeal with the £20,000 reward could finally help us secure justice for Joy."

Police were originally called by the London Fire Brigade at 11.45pm on October 17, 1995 to reports of a fire at a sixth floor flat.

Firefighters broke into the premises and discovered Joy's injured body in the bedroom of her Walthamstow flat.

Two smouldering fires, deliberately started in the bedroom and another in the lounge, had to be extinguished.

A post mortem examination, held at the Queen's Road Mortuary in Walthamstow, revealed the cause of death to be multiple injuries, including a number of stab wounds to the chest area.

The pathologist also indicated that Joy had been sexually assaulted prior to her death.

Following numerous police appeals detectives were able to piece together Joy's last movements.

Officers are aware that Joy visited the London Healing Mission, in Notting Hill, on the afternoon she was murdered.

She carried out voluntary work at the centre and was seen by a colleague leaving the Mission at around 3.30pm.

She headed towards Pembridge Road before visiting a chemist close to her home address in Wood Street, Walthamstow at 5.50pm.

A neighbour at St. David's Court confirmed hearing loud noises or banging coming from Joy's flat at around 10.30pm.

At 11.18pm on October 17, 1995 a phone call was made from a public telephone box along Fulbourne Road, Walthamstow.

A man was requesting assistance from the London Fire Brigade, having seen smoke coming from Joy's flat.

Police made numerous appeals to trace this caller but he is still being sought as part of the investigation as he could hold vital clues.

While on the phone the caller can be heard asking someone what road they were standing in to assist the emergency call handler.

He was speaking to someone who was standing in a queue for a bus.

This person is yet to be located.

In addition to these two people police are also releasing a CCTV image of a man they would like to trace.

He was captured as he entered the front of St David's Court at around 10.30pm.

He is white, aged between 30 to 40 years, although will now be aged between 50 and 60 years, with short hair.

He was wearing a light-coloured jacket.

Anyone with any information is asked to contact the Incident Room on 020 7230 7963, or to remain anonymous, call Crimestoppers on 0800 555 111."

A BBC Crimewatch appeal is due to broadcast on BBC1 today (December 14) at 9pm.